[Qemu-devel] [PATCH v5 02/12] qcow2: Implement bdrv_make_empty()

[Max Reitz]

Implement bdrv_make_empty() by making all clusters in the image fall
through to the backing file (via the now modified discard).

Signed-off-by: Max Reitz <mre...@redhat.com>
---
 block/qcow2.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index 1e7b7d5..4d70665 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2006,6 +2006,27 @@ fail:
     return ret;
 }
 
+static int qcow2_make_empty(BlockDriverState *bs)
+{
+     uint64_t start_sector;
+     int ret = 0;
+
+     /* The step taken here may not exceed INT_MAX when multiplied by
+      * BDRV_SECTOR_SIZE. 64k is arbitrary, but works well. */
+     for (start_sector = 0; start_sector < bs->total_sectors;
+          start_sector += 65536)
+     {
+         ret = qcow2_discard_clusters(bs, start_sector * BDRV_SECTOR_SIZE,
+                 MIN(65536, bs->total_sectors - start_sector),
+                 QCOW2_DISCARD_REQUEST, true);
+         if (ret < 0) {
+             break;
+         }
+     }
+
+     return ret;
+}
+
 static coroutine_fn int qcow2_co_flush_to_os(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
@@ -2388,6 +2409,7 @@ static BlockDriver bdrv_qcow2 = {
     .bdrv_co_discard        = qcow2_co_discard,
     .bdrv_truncate          = qcow2_truncate,
     .bdrv_write_compressed  = qcow2_write_compressed,
+    .bdrv_make_empty        = qcow2_make_empty,
 
     .bdrv_snapshot_create   = qcow2_snapshot_create,
     .bdrv_snapshot_goto     = qcow2_snapshot_goto,
-- 
1.9.2